With the market demand for projection apparatus's brightness, color saturation, service life, non-toxic environmental protection and so on, the types of light sources used by projection apparatuses have evolved from ultra-high pressure mercury lamps (UHP lamps), light emitting diodes (LEDs), to laser diode (LD) light sources.
Currently, the cost of high-brightness red laser diodes and green laser diodes is too high. In order to reduce costs, blue laser diodes are generally used to excite phosphors on phosphor wheels to generate yellow light and green light. The desired red light is filtered through a filter wheel, and blue light emitted by a blue laser diode is combined to form the three primary colors of red, green and blue required for the projection image.
The phosphor wheel is an important element in a projection apparatus using a laser diode as a light source. It is responsible for converting the blue light emitted from the blue laser diode into yellow light and green light, or reflecting or allowing the blue light to pass therethrough. In a conventional phosphor wheel capable of reflecting blue light, a phosphor layer is provided on the turntable of the phosphor wheel, and the turntable has openings for disposing reflective glass. Since the reflective surface of the reflective glass and the surface of the turntable on which the phosphor layer is disposed are generally in the same plane, the surface of the phosphor layer is higher than the reflective surface of the reflective glass. In some optical designs and applications, the incident blue light cannot be focused on the phosphor layer, resulting in poor wavelength conversion efficiency.
The information disclosed in this “BACKGROUND OF THE INVENTION” section is only for enhancement understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Furthermore, the information disclosed in this “BACKGROUND OF THE INVENTION” section does not mean that one or more problems to be solved by one or more embodiments of the invention were acknowledged by a person of ordinary skill in the art.